Can I use a panoramic rendered Blender scene as environment texture?
This should definitely be possible. Pre-rendered backgrounds are a pretty common technique for speeding up rendering times.

The only issue to be aware of with static backgrounds is that you need to be careful with camera movement as you will not get the parallax effect. I suspect that this is likely to be more obvious in VR scenes due to independent head movement/viewing angle (you can just get away with panning a few layers over each other at different rates). How noticeable this effect is will depend on the distance between the camera and the nearest object in the background, the variation of object distances in the background and the amount of camera movement.